1. Field of the Invention
The present invention relates to a magneto-optical recording apparatus recording a signal onto a magneto-optical recording medium, and a magneto-optical recording method.
2. Description of the Background Art
Attention is focused on a magneto-optical recording medium as a rewritable recording medium of great storage capacity and high reliability. The magneto-optical recording media are now applied as computer memories and the like. Standardization of a magneto-optical recording medium having a storage capacity of 6.0 Gbytes (AS-MO (Advanced Storage Magneto-optical Disk) standard) is in progress to be provided for actual usage. This magneto-optical recording medium of high density has the signal reproduced by the MSR (Magnetically Induced Super Resolution) method. More specifically, a laser beam is projected to transfer the magnetic domain of the recording layer of the magneto-optical recording medium to a reproduction layer and also forming a detection window in the reproduction layer to allow detection of only the transferred magnetic domain. The transferred magnetic domain is detected from the formed detection window.
Also, a magnetic domain enlargement reproduction technique has been developed. An alternating magnetic field is applied in reproducing a signal from a magneto-optical recording medium. The magnetic domain of the recording layer is enlarged to the reproduction layer by the laser beam and the alternating magnetic field while transferring to reproduce a signal. A magneto-optical recording medium that can record or reproduce signals of 14 Gbytes by virtue of this technology has been proposed.
In recording a signal onto such a magneto-optical recording medium, a pulsed laser beam is directed onto the magneto-optical recording medium. A magnetic field modulated according to the record signal is applied onto the magneto-optical recording medium. A magnetic head drive signal that generates a magnetic field modulated according to the record signal is generated delayed by a predetermined time with respect to the laser drive signal that generates a pulsed laser beam.
In the conventional magneto-optical recording, the delay time of the magnetic head drive signal with respect to the laser drive signal is defined constant even if the power of the laser beam is altered. There may be the case where application of the magnetic field to the magneto-optical recording medium ends during the period the temperature of the magneto-optical recording medium is boosted higher than the Curie temperature. In this case, a domain having the desired length cannot be formed. There was a problem that a signal could not be recorded correctly. This tendency is particularly noticeable in forming a domain of short domain length.
An object of the present invention is to provide a magneto-optical recording apparatus and method that allows a signal to be recorded correctly on a magneto-optical recording medium.
According to an aspect of the present invention, a magneto-optical recording medium includes an optical head, a magnetic head, a drive signal generation circuit, a laser drive circuit, a magnetic head drive circuit, and a phase difference control circuit. The optical head includes a laser generating a pulsed laser beam to be directed onto a magneto-optical recording medium. The magnetic head applies a magnetic field on the magneto-optical recording medium. The drive signal generation circuit generates a laser drive signal and a magnetic head drive signal. The laser drive circuit drives the laser in response to a laser drive signal. The magnetic head drive circuit drives the magnetic head in response to a magnetic head drive signal. The phase difference control circuit controls the phase difference between the laser drive signal and the magnetic head drive signal.
Preferably, the magneto-optical recording apparatus further includes an error correction circuit and a phase difference optimization circuit. The error correction circuit corrects error of a magneto-optical signal applied from the optical head. The phase difference optimization circuit optimizes the phase difference according to the error rate applied from the error correction circuit.
Further preferably, the phase difference control circuit alters the phase difference by every predetermined amount. The phase difference optimization circuit includes an error rate detection circuit and a determination circuit. The error rate detection circuit detects the error rate when the error correction circuit corrects the error of a signal recorded and reproduced with each altered phase difference. The determination circuit determines the optimum phase difference according to the detected error rate.
According to the present invention, a pulsed laser beam is directed onto a magneto-optical recording medium, and a magnetic field is continuously applied to the magneto-optical recording medium until the temperature of the magneto-optical recording medium reaches the maximum temperature exceeding the Curie temperature and then falls to the Curie temperature again. The direction of the magnetic field is inverted after the temperature of the magneto-optical recording medium becomes lower than the Curie temperature. As a result, the signal is recorded in fidelity onto the magneto-optical recording medium.